The MPLS WG Archive

[Eric Osborne <eosborne@cisco.com>]

On Fri, May 31, 2002 at 11:41:35AM -0700, Shahram Davari wrote:
> Vijay,
> 
> I know all this. The question was: 
> 
> "Why use LDP instead of IP?". 
> 
> If you have an answer please provide.

(coming back from vacation)
Another answer that I haven't seen here is the ability to do cell-mode
MPLS with ATM.  That's one of the original MPLS applications, and LDP
certainly helps with that.




eric

> 
> -Shahram
> 
> > -----Original Message-----
> > From: Vijay Bollapragada [mailto:vbollapr@cisco.com]
> > Sent: Friday, May 31, 2002 2:34 PM
> > To: Shahram Davari
> > Cc: 'mpls@uu.net'; 'ppvpn@ppvpn.francetelecom.com'
> > Subject: RE: Basic LDP Question
> > 
> > 
> > On Fri, 31 May 2002, Shahram Davari wrote:
> > 
> > > Vijay,
> > 
> > > But LDP does not give you the TE ability. So why use LDP?
> > 
> > Agreed, that LDP does not give the ability to do TE, I only 
> > said use MPLS
> > in the core, not necassarily LDP :-) but in any case, Here is 
> > what 2547
> > draft says about using LDP for the top label..
> > 
> > Section 4.3.2
> > 
> > "All that matters for the VPN architecture is that some label switched
> > path between the router and its BGP next hop exists.  
> > However, to ensure
> > interoperability  among systems which implement this VPN architecture,
> > all such systems must support LDP [MPLS-LDP]."
> > 
> > Of course, once could use many other mechanisms to get the vpn_labeled
> > packet from one edge PE to another edge PE, Interoperability 
> > is the key
> > here.
> > 
> > Thanks,
> > Vijay
> > 
> > 
> > 
> > > 
> > > > -----Original Message-----
> > > > From: Vijay Bollapragada [mailto:vbollapr@cisco.com]
> > > > Sent: Friday, May 31, 2002 2:06 PM
> > > > To: Shahram Davari
> > > > Cc: 'mpls@uu.net'; 'ppvpn@ppvpn.francetelecom.com'
> > > > Subject: Re: Basic LDP Question
> > > > 
> > > > 
> > > > In the 2547 case, typically u have 2 labels, the vpn_label 
> > > > (bottom label)
> > > > and the top label is the label to get the packet to the far 
> > > > end PE, Now,
> > > > LDP is used for this top label.
> > > > 
> > > > I think u are questioning why use LDP for this bottom_label 
> > > > and why not
> > > > simply encapsulate the MPLS packet in IP to get the packet to 
> > > > the next_hop
> > > > PE. If this is your Q, You are absolutely correct and 
> > this is what the
> > > > following draft talks about
> > > > 
> > > > http://search.ietf.org/internet-drafts/draft-ietf-ppvpn-gre-ip
> > > > -2547-01.txt
> > > > 
> > > > IMHO, this is certainly do-able but MPLS in the core give us 
> > > > the ability
> > > > to do things like Traffic Enginnering
> > > 
> > > 
> > > -Shahram
> > > 
> > >  which are quite a challenge over
> > > > pure IP.
> > > > 
> > > > Thanks,
> > > > Vijay
> > > > 
> > > > 
> > > > 
> > > > On Fri, 31 May 2002, Shahram Davari wrote:
> > > > 
> > > > > Hi,
> > > > > 
> > > > > What problem a mp2p LDP-based MPLS network is trying to 
> > > > solve (like the one used in RFC2547) that can't be done with 
> > > > pure IP forwarding?
> > > > > 
> > > > > Note: Don't tell me fast forwarding, because we can do fast 
> > > > IP lookup as well.
> > > > > 
> > > > > Yours,
> > > > > Shahram
> > > > > 
> > > > > 
> > > > 
> > > 
> >